this is not normal and its a fairly simple low poly scene as well with no textures and materials yet. i have multi res for some sculpts but even when its off it lags like crazy. i have done far more complicated projects that took up a fraction of the file space. i have compress files enabled by default, looked through the outliner and see nothing unusual, even tried appending everything into a new file and it was still the same. please help because working on it is almost impossible and i need to finish it for my assignment.
The scene takes up almost 2 GB RAM, if you are indeed using an old laptop, this might be the bottleneck, especially if you have a web browser open with a few tabs, too. In windows you should always have an eye on the task manager, especially the performance tab.
As Anders, I would not call this low poly aswell, with almost 50k polygons. That is why rob suggested to delete the heads, as they are making up the majority of those. You could however dissolve a lot of edges, too...
Hmm.. I don't have any problem playing around in your scene. You are sure you don't have anything else running on your pc. And what is your PC speccs for that matter? I would not call the scene low poly. Have you applied any subdivision surface modifier to the models, because they are smoothed out and have a lot of faces, that would make the models horrible to work on, if you need to change anything?
I am writing this in Answer, because I don't have enough reputation to just comment on your post. Hope this could help you, please reply back to my questions and I'll try help you out :)
Best regards Anders